The principal objective of this research is to develop implantable bioerodible drug delivery devices that will release insulin in response to external glucose concentration. The delivery device consists of a bioerodible polymer containing dispersed insulin surrounded by a hydrogel containing immobilized glucose oxidase. The polymer containing dispersed insulin solubilizes by protonation of amine function and is designed so that the rate of solubilization increases with decreasing external pH. At a normal 100 mg% plasma glucose concentration, glucose will diffuse into the hydrogel and be oxidized by glucose oxidase to gluconic acid, which will then diffuse out of the hydrogel. As a consequence of that process, an equilibrium gluconic acid concentration will be maintained within the hydrogel and the polymer will erode at a constant rate. That erosion rate will be chosen so that an appropriate amount of insulin is released to maintain normal glucose levels in a diabetic patient. When the glucose level rises above 100 mg%, the equilibrium within the hydrogel will be disturbed and the pH will drop. This will result in faster erosion and, hence, faster release of insulin. This spike in insulin delivery will then lower the blood glucose level to the normal 100 mg%.